It is currently common practice to use duplexers in all microwave link systems. The vast majority of them make use of waveguide accesses at two different polarities, or else they make use of coaxial accesses on rectangular or square horns. They are generally based on the principle that an over-size waveguide is capable of propagating two waves at orthogonal polarizations (this applies in particular to a circular or a square TE 11 waveguide).
The electromagnetic fields are separated by a mode filtering effect (for example using a decoupling plate which puts one of the types of propagation below a cut-off) in combination with lengths of waveguide.
In principle, a good quality duplexer provides 40 dB to 50 dB of decoupling between accesses, and it must be made as a waveguide at all of its accesses for the purpose of preserving the distribution of the electromagnetic fields. This principle is always used because of its greater fidelity in reproduction and its improved symmetry.
In present-day international competition, data transmission systems include retransmission via satellites operating in communication with cheap miniature ground stations. TV retransmission by such systems appears to be headed for great expansion.
Technical progress, for example in the following fields:
monolithic circuit manufacture using silicon (Si) or gallium arsenide (GaAs);
automatic wiring of circuits using surface mounting components; and
computer-assisted circuit design;
makes it possible, cheaply and on a large scale, to achieve reliable semiconductor circuits of the following types: high power amplifiers (HPA); low noise amplifiers (LNA); and low noise converters (LNC).
In this case, competition resides in the mechanical environment which makes use of cast metal boxes and also of hybrid or composite technologies.
U.S. Pat. No. 4,156,089 describes a system for receiving linear orthogonal polarized microwave signals, which system is essentially constituted, after a parabolic reflector, by a receive horn, a bandpass filter, a mode separator, and a housing containing electronic circuits for amplification and frequency conversion. The horn and the filter are made as waveguides and, together with the mode separator and the housing, are carried by a common support constituted by two half-shells which are symmetrical about their longitudinal assembly plane and which are suitable for being manufactured by a common industrial method, in particular a method such as casting or injecting a metal or a plastic material which is subsequently metallized.
However, in such a system, the connection between the portion made of waveguide and the electronic circuits is provided by subdividing the separator into two waveguides of orthogonal rectangular right cross-sections; with these two waveguides being coupled to two respective circuit support plates.
Such an implementation prevents a high degree of integration because of the existence of problems of field deformation by coupling between the orthogonally polarized microwave signals.
The object of the present invention is to mitigate these drawbacks.